Hi Sqwheels! Whew, I was a bit behind. I have a few thoughts - first, don't worry about what looks like mold on the root riot plugs - I use similar plugs, and they sometimes grow a harmless fungus, but it is harmless. They do come with beneficials and micro nutes somewhat built in, and that happens sometimes. Scared me too at first though!
Ultimately for water, I would recommend saving for or buying an RO unit if you can. I put it off for the longest time (my water is like yours quite a bit from the sounds of it), but finally got one. It was around $200 or so. Hydrologic Stealth 150, I think? The 150 means it will make 150 gallons per day, in an ideal situation. Mine does about 50 due to low water pressure, but that's still plenty.
It is relatively small (about the size of a briefcase), and it hooks up and unhooks very simply - most lines just "push" in. My PPM's now measure between 0-10. The only thing I don't like is that it does "waste" a fair amount of water. I hook it up to a large rubbermaid container and fill it up with an extra 25+ gallons to always have at the ready. (I go through it in less than a week with my current set-up).
I somehow had it in my mind it was a much bigger deal to do, and I should have done it a lot earlier, but I didn't realize how simple it would be. I keep it next to my utility sink in the basement on a little shelf, and hooking it up takes 30 seconds or so, as does unhooking. I "make" water once a week, and then I don't even have it hooked up other days. Easy breezy.
I know that you have unique challenges physically, so not sure how that would play into it, but it's the best solution for you if you continue growing long term, can handle it physically, and afford it. It makes my life so much easier for me!!
Sorry if this has come up and I forgot - but you just have such a similar water issue as mine, and everything short of a system like I'm talking about probably won't work (Brita, etc. just won't cut it for lowering the PPMs, though they'll make you nice drinking water)
Oh, one other thing - if you have clean air in your home, a dehumidifier makes excellent water for your plants. And, they often need lowered humidity during flower cycle anyway... Just beware that if there is nicotine smoke in the air, it can be a toxic additive to the dehumidifier water...
Hope you are doing well, Sqwheels!
EDIT - here's a pic of a RO unit similar to mine (I think this one does 250gph):